Energy Recovery System

ABSTRACT

An energy recovery system ( 10 ) including a structure ( 12 ) including at least a boundary ( 14 ) area made of a material which is substantially transparent to solar radiation, thus to capture solar energy in the internal environment of the structure, a heat pump ( 19 ) including a closed fluid circuit ( 16 ) which includes a first heat exchanger ( 18 ) in which heat from the internal environment of the structure ( 12 ) is transferred to the fluid, a second heat exchanger ( 20 ) in which heat from the fluid is transferred to a heat energy store ( 24 ), and an impeller ( 22 ) for moving the fluid from the first heat exchanger ( 18 ) where the fluid is at a generally lower pressure to the second heat exchanger ( 20 ) where the fluid is at a generally higher pressure, power to drive the impeller ( 22 ) being derived solely from the energy stored.

The present invention relates to an energy recovery system, particularly but not exclusively for use in relation to the recovery of heat energy from a greenhouse.

It is known that greenhouses or glasshouses having boundaries of which at least a part is made from a material which is transparent to solar radiation, are able to capture the energy inside the greenhouse, as a result of the wavelength of the solar radiation increasing to a length that is unable to pass back through the material of the greenhouse boundary. Thus the temperature of the air inside the greenhouse is caused to rise. Greenhouses are often used to promote the growth of plants and can be built on a large scale for the growth of plants for commercial use. It is known that the rise in air temperature inside the greenhouse can reach undesirable levels which are prejudicial to the growth of plants, for example during the summer, and at such times it is desirable to extract some of the heat from the air in the greenhouse. It is known to store this extracted energy in an underground aquifer such that the energy can be returned to the greenhouse when the amount of solar radiation reaching the greenhouse is smaller, for example during the night, or during the winter.

According to a first aspect of the present invention, there is provided an energy recovery system including a structure including at least a boundary area made of a material which is substantially transparent to solar radiation, thus to capture solar energy in the internal environment of the structure, a heat pump including a closed fluid circuit which includes a first source heat exchanger in which heat from the internal environment of the structure is transferred to the fluid, a second sink heat exchanger in which heat from the fluid is transferred to a heat energy store, and an impeller for moving the fluid from the first heat exchanger where the fluid is at a generally lower pressure to the second heat exchanger where the fluid is at a generally higher pressure, power to drive the impeller being derived solely from the energy stored.

So that the temperature of the air in the structure does not rise to undesirable levels, it is advantageous to be able to use the energy recovery system to capture and store excess solar energy in the form of heat. The stored energy can then be utilised to provide power to the impeller of the heat pump. Excess energy which is not required to provide power to the impeller of the heat pump may be converted into electrical energy and transferred away from the system to power, or assist in powering, other devices. Alternatively, some or all of the stored energy may be used in other applications, for example for domestic or district heating.

The structure is preferably a greenhouse.

The ‘insolation’ (INcoming SOLar radiATION) received at ground level varies with latitude. For example, the solar radiation intensity at latitude of approximately 52° N is approximately 1050 KWhm⁻² per year, whereas at latitude of approximately 0° N, the solar radiation intensity is approximately 2000 KWhm⁻² per year. Therefore the amount of electrical energy generated will also vary with the latitude. However the electrical energy yield is likely to be high, regardless of latitude.

The impeller of the heat pump may be driven by an electrically operated device, electrical energy for operating the device being derived from the heat energy stored. The system may thus include an electrical generator for generating electrical energy from the stored heat energy. The electrical generator may be steam driven, the steam being produced by heating water using the stored heat energy.

Alternatively, the electrical generator may include a turbine which is driven by an organic working fluid. The temperature of the organic fluid may be raised by heat exchange with water. The temperature of the water may be raised by the stored heat energy.

The electrical energy generated may be used directly to operate the electrically operated device to drive the impeller of the heat pump.

Alternatively the system may include an apparatus for using at least part of the electrical energy generated to produce hydrogen gas, and a feed for the hydrogen gas to a hydrogen-gas-using device which drives the impeller of the heat pump. The apparatus for producing the hydrogen gas may include an electrolytic cell, which is able to dissociate the hydrogen and oxygen in water, when a current is passed between an anode and a cathode.

The device which drives the impeller of the heat pump may be an internal combustion engine in which the hydrogen gas is burned as fuel. In this case, the dissociated hydrogen gas and oxygen gas are preferably recombined to enable controlled combustion in the engine. Alternatively, the device which drives the impeller is an electrical motor, there being a fuel cell which uses the hydrogen provided by the electrolysis process as fuel to produce electrical energy to drive the motor.

The energy recovery system may include an apparatus for transferring electrical energy which is not required to drive the impeller of the heat pump, away from the system in order to power other electrical devices. The electrical energy may be transferred to an electrical supply grid, for example.

According to a second aspect of the invention, there is provided a method of recovering energy from a structure including the steps of providing a heat pump for transferring heat from the internal environment of the structure to fluid in a closed fluid circuit of the heat pump, via a first heat exchanger, the heat pump including an impeller for moving the fluid to a second sink heat exchanger, transferring heat from the fluid in the closed fluid circuit to a heat energy store, and utilising the heat stored in the heat energy store to power the impeller of the heat pump.

The method may include the steps of generating electrical energy using the heat energy stored, and using the electrical energy to operate a device for driving the impeller of the heat pump.

The method may include generating electricity by use of a steam turbine, the steam being produced by using the heat energy stored to heat water.

The method may alternatively include using the heat energy stored to raise the temperature of an organic working fluid, and using the organic working fluid to drive a turbine. This is advantageous in situations where the heat energy stored may not be sufficient to produce the desired amount of steam. In such cases, water, the temperature of which has been raised, at least slightly, may be used effectively to raise the temperature of a high molecular mass organic fluid. Thus enabling electrical energy to be produced even when the energy stored is only sufficient to raise the temperature of the water in the heat energy store by a relatively small amount.

The method may include the step of using the electrical energy generated directly to power the device which drives the impeller.

The method may further include the steps of using the electrical energy generated in an apparatus to produce hydrogen gas, and supplying the hydrogen gas to the device which is operable to drive the impeller of the heat pump. The hydrogen gas may be produced by electrolysis of water.

The device provided to drive the impeller of the heat pump may be a fuel cell, which is able to produce electrical energy using the hydrogen produced by electrolysis as fuel.

The method may include combining the hydrogen gas with oxygen, supplying the mixture of oxygen and hydrogen to an internal combustion engine and operating the internal combustion engine to drive the impeller of the heat pump.

The method may be for recovering heat from a greenhouse.

Embodiments of the invention will now be described, by way of example only, with reference to the following drawings, of which:

FIG. 1 shows an energy recovery system according to the present invention, and

FIG. 2 shows an alternative embodiment of the energy recovery system.

Referring to FIG. 1, there is shown an energy recovery system 10 including a structure 12 having a boundary 14 at least a part of which includes a material which is substantially transparent to solar radiation, for example glass or plastic. The boundary 14 preferably includes a plurality of walls and a roof, each of which may include transparent material. In this example, the structure 12 is a greenhouse. The system 10 also includes a heat pump 15 for transferring heat energy to a heat energy store 24 from the internal environment of the greenhouse 12.

The heat pump 15 includes a closed fluid circuit 16 around which heat exchange fluid, for example water, or a water-anti-freeze mixture, is circulated.

The heat pump 15 includes a first source heat exchanger 18, and a second sink heat exchanger 20 within the circuit 16. The circuit 16 also includes an impeller 22 which circulates heat exchange fluid around the circuit 16, between the first heat exchanger 18 and the second heat exchanger 20, and an expansion valve 19 for reducing the pressure in the heat exchange fluid between the second sink heat exchanger 20 and the first source heat exchanger 18. The impeller 22 is powered by a device 28. The device 28 may be a motor or a gas engine. The gas engine 28 may be, for example, an internal combustion engine, which is also preferably housed within the greenhouse 12.

The second sink heat exchanger 20 is in thermal communication with a heat energy store 24. In the present example the heat energy store 24 includes a tank which is used to hold water at high pressure, the pressure of the water increasing as a result of an increase in temperature of the water arising from the thermal communication between the sink heat exchanger 20 and the tank 24. The tank 24 includes an outlet 26, through which steam (or high temperature water) is releasable.

The system 10 also includes a generator 30 for generating electricity by utilising the steam or high temperature water supplied by the heat energy store 24. The generator 30 may be of any suitable type, and may include, for example, a binary turbine and a two-phase expander or a Stirling engine. Alternatively, the generator 30 may include low pressure condensing extraction turbines, or may include a thermoelectric generator which operates according to the Seebeck effect, such as one available from Varmaraf ehf or Power Chips plc.

The system 10 further includes an electrolytic cell 32 which is electrically connected to the generator 30. The electrolytic cell 32 is coupled to the device 28, by a feed 29 such that hydrogen gas produced during electrolysis of water may be transferred to the device 28, as described in more detail below.

The system 10 also includes apparatus 34 for transferring excess electrical energy, which is not used in the electrolysis process to make gas for the device 28, away from the system 10, to an electrical supply grid 36. Alternatively, the excess electrical energy can be used in further electrolytic processes, as described in more detail below.

In use, the greenhouse 12 receives solar radiation which increases the temperature of the internal environment of the greenhouse 12. Energy is transferred as heat from the internal environment of the greenhouse 12 to the heat exchange fluid in the circuit 16. The heated heat exchange fluid is pumped from the first source heat exchanger 18 around the fluid circuit 16 to pressurise and heat the fluid. Thus, the pressure of the heat exchange fluid in the circuit 16 is greater in the second sink heat exchanger 20 than the pressure of the fluid when it is in the first sink heat exchanger 18. Energy is transferred in the form of heat from the heat exchange fluid by the second, sink heat exchanger 20 to the pressurised water in the heat energy store 24. Thus the temperature of the water in the heat energy store 24 rises, for example to between 95° and 100° C. The temperature may exceed 100° C. The heat exchange fluid is returned from the second heat exchanger 20 to the first heat exchanger 18 via the expansion valve 19 which reduces the pressure of the heat exchange fluid to enable the fluid to take in further energy. This enables the temperature of the air inside the greenhouse 12 to be maintained, or otherwise controlled, as required.

The tank of the heat energy store 24 is able to hold the heated water at high pressure. The amount of stored energy is greater than the amount of energy required to power the heat pump, and is dependent on the capacity of the heat energy store 24 and on the coefficient of performance of the heat pump.

Steam (or high temperature water, as described in more detail below) is releasable from the tank 24 to be supplied to the generator 30. The generator 30 uses the energy stored in the hot water or steam to generate electricity, using known methods, for example using the energy of the steam to drive a turbine.

In circumstances where storing sufficient energy to produce a useable quantity of steam would be problematic, the steam-driven generator 30 may be replaced by a generator which operates according the Organic Rankine Cycle (ORC). In this case, heated water, rather than steam, is released from the heat energy store 24. The heated water is used to raise the temperature of a high molecular mass organic working fluid. The organic fluid is used to drive a turbine, to generate electrical energy. The working fluid is selected to exploit efficiently the temperature of the heated water to produce electricity.

In the present example, the electrical energy generated by the generator 30 is used in the electrolytic cell 32 to electrolyse water to produce hydrogen gas, with a by-product of oxygen gas. The oxygen by-product can either be used in its isolated form, for example in medical or chemical applications, or can be recombined with the hydrogen gas and conveyed as fuel for the device 28, for example for combustion therein to drive the impeller 22 of the heat pump 15. Alternatively, the device 28 which drives the impeller 22 may be fuel cell to which the hydrogen gas may be supplied in its isolated form.

Surplus electrical energy which is not required to carry out the electrolytic process may be transferred away from the system 10, for example to an electricity supply grid.

The cycle is continuous, and is largely self-sustaining. The energy required to operate the impeller 22 of the heat pump 15 is derived from the solar energy stored by the system itself as heat. Solar radiation and water are required to be input to the cycle in order for the cycle to continue.

It is preferable to contain as much of the energy recapture system 10 within the greenhouse 12 as possible. However, it will be appreciated that limitations on space may mean that if the heat energy store 24, for example, is large, it has to be housed outside of the greenhouse 12. Regardless of its position, it is advantageous to insulate thermally the heat energy store 24, to inhibit loss of energy from the system 10 to the environment. Housing the heat pump 15 and the device 28 for driving the impeller 22 of the heat pump 15, at least, inside the greenhouse 12 enables the efficiency of the system to be optimised, since if the device 28 is a gas engine, for example, any exhaust gases from the engine 28 will be contained within the greenhouse, and the heat ‘lost’ from the engine 28 will act to increase the temperature of the air inside the greenhouse, and as such the energy may be recaptured by the heat pump 15. Housing the generator 30 inside the greenhouse 12 would also mean that any heat losses incurred by the generator 30 can be recaptured by the heat pump 15. However it is envisaged that it is possible to operate an ORC system without any heat loss from the ORC apparatus.

FIG. 2 shows an alternative embodiment of the invention which includes an energy recovery system 110 which is similar to the energy recovery system 10. Features of the system 110 which correspond with features of the system 10 have similar reference numerals, but include the prefix ‘1’. The energy recovery system 110 is for a structure 112 having a boundary 114, a part of which is or includes a material which is transparent to solar radiation. The structure 112 is, in this example, a greenhouse. The system 110 also includes a heat pump 115, which includes a closed fluid circuit 116. The heat pump 115 is housed inside the greenhouse 112 and includes a first source heat exchanger 118, and a second sink heat exchanger 120 in the circuit 116. The heat pump 115 also includes an impeller 122 for circulating heat exchange fluid, for example water, or a water-anti-freeze mixture, around the circuit 116, between the first source heat exchanger 118 and the second sink heat exchanger 120. The impeller 122 is powered by an electrically operated device, for example a motor 128. The heat pump 115 also includes an expansion valve 119 for reducing the pressure in the heat exchange fluid between the second sink heat exchanger 120 and the first source heat exchanger 118.

The circuit 116 is preferably housed within the greenhouse 112. The second sink heat exchanger 120 is in thermal communication with a heat energy store 124, which may be a tank similar to the tank 24 described in relation to system 10.

The system 110 may also include a generator 130 for utilising high temperature water or steam from the tank 124 to generate electricity. A proportion of the electrical energy generated is used directly to operate the motor 128 to drive the impeller 122 of the heat pump 115. Electrical energy which is not required to power the motor 128 may be transferred to an electricity supply grid by transfer apparatus 134, for example via current conducting cables.

In relation to both of the recovery systems 10, 110, it will be apparent that the heat energy stored in the heat energy store 24, 124 may be used in applications other than the generation of electricity. For example, the heat stored may be used for domestic or district heating. District heating is a system for distributing heat generated in a central location for residential and commercial heating requirements. In the case of a domestic greenhouse, rather than a commercial scale greenhouse, the heat energy store 24, 124 may store sufficient energy to provide heating for a home, or to supplement an existing home heating system.

It is anticipated that the system 10, 110 will include a computerised process and/or climate control system which is operable to control the operation of the system 10, 110 in order to maintain or alter the temperature of the air inside the greenhouse 12, 112 as required.

It is envisaged that at times when the temperature externally of the greenhouse 12 is higher than the desired air temperature inside the greenhouse 12, the systems 10, 110 may include a heat exchanger externally of the greenhouse, for transferring heat from outside the greenhouse 12 to the heat energy store 24. The heat exchange surface may be a part of the boundary area 14, 114 which defines the interior of the greenhouse 12, 112.

The system 10, 110 may include automated cleaning equipment, to clean the transparent material which is included in the boundary area 14, 114 of the greenhouse 12, 112, such that the amount of solar radiation entering the greenhouse 12, 112 can be maximised.

It is also envisaged that a conventional boiler may be included in the system 10, 110, to raise the temperature of the water in the heat energy store 24, 124 initially, to prime the system 10, 110.

A further advantage of the heat recovery system 10, 110 is that the internal temperature of the greenhouse 12, 112 can be maintained at a lower temperature than the air temperature externally of the greenhouse 12, 112. For example the internal temperature may be maintained at approximately 0° C. or 1° C. Thus condensation will form on the outer surface of the boundary area. The condensation can be collected to provide a supply of fresh condensate water.

A further advantage of the heat recovery system 10, 110 is that the internal temperature of the greenhouse 12, 112 can be maintained at the lower temperature than the air temperature externally of the greenhouse. For example, the internal temperature may be maintained at approximately 0° C. or 1° C. Thus condensation will form on the outer surface of the boundary area. The condensate can be collected to provide a supply of fresh condensate water.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. 

1. An energy recovery system including a structure including at least a boundary area made of a material which is substantially transparent to solar radiation, thus to capture solar energy in the internal environment of the structure, a heat pump including a closed fluid circuit which includes a first source heat exchanger in which heat from the internal environment of the structure is transferred to the fluid, a second sink heat exchanger in which heat from the fluid is transferred to a heat energy store, and an impeller for moving the fluid from the first heat exchanger where the fluid is at a generally lower pressure to the second heat exchanger where the fluid is at a generally higher pressure, power to drive the impeller being derived solely from the energy stored.
 2. An energy recovery system according to claim 1 wherein the structure is a greenhouse.
 3. An energy recovery system according to claim 1 wherein the impeller is driven by an electrically operated device, electrical energy for operating the device being derived from the heat energy stored.
 4. An energy recovery system according to claim 3 wherein the system includes an electrical generator for generating electrical energy from the stored heat energy.
 5. An energy recovery system according to claim 4 wherein the electrical generator is steam driven, the steam being produced by heating water using the stored heat energy.
 6. An energy recovery system according to claim 4 wherein the electrical generator includes a turbine which is driven by an organic working fluid.
 7. An energy recovery system according to claim 4 wherein the electrical energy generated is used directly to operate the electrically operated device to drive the impeller of the heat pump.
 8. An energy recovery system according to claim 1 wherein the system includes an apparatus for using at least part of the electrical energy generated to produce hydrogen gas, and a feed for the hydrogen gas to a device which drives the impeller of the heat pump.
 9. An energy recovery system according to claim 8 wherein the apparatus for producing hydrogen gas includes an electrolytic cell.
 10. An energy recovery system according to claim 8 wherein the device which drives the impeller of the heat pump is an internal combustion engine.
 11. An energy recovery system according to claim 8 wherein the device which drives the impeller is a fuel cell.
 12. An energy recovery system according to claim 4 including apparatus for transferring electrical energy which is not required by the impeller of the heat pump away from the system in order to power other electrical devices.
 13. (canceled)
 14. A method of recovering energy from a structure including the steps of providing a heat pump for transferring heat from the internal environment of the structure to fluid in a closed fluid circuit of the heat pump, via a first heat exchanger, the heat pump including an impeller for moving the fluid to a second sink heat exchanger, transferring heat from the fluid in the closed fluid circuit to a heat energy store, and utilising the heat stored in the heat energy store to power the impeller of the heat pump.
 15. A method of recovering energy according to claim 14, wherein the structure is a greenhouse.
 16. A method of recovering energy from a structure according to claim 14 including the steps of generating electrical energy using the heat energy stored, and using the electrical energy to operate a device for driving the impeller of the heat pump.
 17. A method according to claim 16 including generating electricity by use of a steam turbine, the steam being produced by using the heat energy stored to heat water.
 18. A method according to claim 16 including using the heat energy stored to raise the temperature of an organic working fluid, and using the organic working fluid to drive a turbine.
 19. A method according to claim 16 including the step of using the electrical energy generated directly to power the device which drives the impeller.
 20. A method of recovering energy from a structure according to claim 16 further including the steps of using the electrical energy generated in an apparatus to produce hydrogen gas, and supplying the hydrogen gas to the device which is operable to drive the impeller of the heat pump.
 21. A method according to claim 20 wherein the hydrogen gas is produced by the electrolysis of water.
 22. A method of recovering energy from a structure according to claim 20 wherein the device provided to drive the impeller of the heat pump is a fuel cell.
 23. A method of recovering energy from a structure according to claim 20 including combining the hydrogen gas with oxygen, supplying the mixture of oxygen and hydrogen to an internal combustion engine and operating the internal combustion engine to drive the impeller of the heat pump.
 24. (canceled)
 25. (canceled) 